Connecting smart cities with 802.11ax APs

The wireless space has evolved considerably since the base version of the IEEE 802.11 standard debuted in 1997 with specifications for just two raw data rates of 1 and 2 megabits per second (Mbit/s). The primary focus of the 802.11 standards has been higher data rates – with the 802.11ac Wave 2 specifications taking Wi-Fi to gigabit speeds.

Connecting smart cities with 802.11ax APs

802.11ax features multiple enhancements to support the latest demands for increased Wi-Fi bandwidth and high quality of service (QoS) in high-density smart city locales.

These include transportation hubs such as airports, bus depots and train stations; streets lined with smart parking spaces, pipes, meters and lights; as well as indoor stadiums and outdoor event grounds that host intense mobile data offloads for users streaming 4K video. In the future, we expect 802.11ax infrastructure to routinely support an even wider range of smart city deployments and applications including sensor-laden roads, air-quality monitors, CCTV and gunshot detection systems for law enforcement officials.

Linking NYC with public Wi-Fi kiosks

From our perspective, reliable connectivity – whether Wi-Fi, CBRS, BLE, Zigbee, Zwave or LoRa – is critical for both smart city infrastructure and applications. As such, it is important for the public and private sectors to collaborate and ensure the delivery of multi-purpose edge connectivity.

An example of a public-private connectivity partnership was highlighted by the LinkNYC rollout of 7,500 free public Wi-Fi kiosks with a 150 feet connectivity radius and support for 250 concurrent devices per kiosk. In addition to Wi-Fi, the sleek kiosks offer multiple services including free domestic phone calls and emergency calls, touchscreen tablets for directory service, access to public and city service announcements and charging stations for mobile devices.

IEEE 802.11ax: Taking a closer look

As we noted above, the new 802.11ax standard offers an enhanced feature set to accommodate high-density access point (AP) deployments in challenging environments such as smart cities.

Specific benefits of the 802.11ax feature set can be broadly categorized in the following areas:

Improvement in network capacity and efficiency

Increase in peak throughputs

Improvement in device battery life

Reliability in outdoor environments

Let’s take a closer look at some key 802.11ax features below.

OFDMA and MU-MIMO

Leveraged from the cellular domain, OFDMA and MU-MIMO are techniques that increase reliability and efficiency in the unlicensed Wi-Fi spectrum. Under OFDMA, the entire channel bandwidth can be divided into smaller sub-channels called Resource Units. The AP decides how to allocate the sub-channels – each RU (or sub-channel) can be addressed to different clients that are serviced simultaneously. Put simply, this improves the average throughput (per user) by creating a narrower, albeit dedicated sub-channel. Moreover, OFDMA boosts spectral efficiency and reduces latency, while supporting heterogeneous users (i.e., IM, email or light web browsing versus large downloads).

It is important to point out that OFDMA and MU-MIMO provide complementary techniques to concurrently serve multiple users. More specifically, OFDMA is best utilized when multiple connections transmit limited amounts of data. OFDMA which is effective at all ranges – close, medium and far – offers lower latency and can be used to mitigate OBSS interference issues. Meanwhile, MU-MIMO best serves multiple user with full buffer traffic. MU-MIMO is most effective at close-to mid-range and tends to increase latency and lacks interference mitigation techniques.

In addition, with 802.11ax, OFDMA and MU-MIMO are supported in downlink (from AP to stations) and uplink (from stations to AP). It should be noted that the AP schedules the transmissions in both directions. This contrasts with pre-802.11ax networks (especially in uplink direction), where resource allocation is contention-based, with individual stations making the decision to grab the medium and transmit data. As stations increase, so does contention.
Sub-carrier spacing and MAC/PHY enhancements

With 802.11ax, sub-carrier spacing is reduced, thereby enabling a 4X jump in the number of available data-tones and significantly increasing maximum PHY rates. Moreover, additional data tones help support multiple users in conjunction with OFDMA. 802.11ax also optimizes spectral efficiency with more tones/channel, reduces overhead, bolsters outdoor operation and facilitates a quantum jump in highest achievable PHY rates. Last, but certainly not least, 802.11ax features a 1024-QAM constellation (in contrast to 256-QAM for 11ac), enabling a 25% data rate increase.

Power efficiency

802.11ax features scheduled sleep and power-on (awake) times, along with pre-negotiated wake times between AP and clients to avoid on-the-air contention amongst client devices. This helps make air utilization more efficient and enhances the battery life of client devices.

In conclusion, 802.11ax addresses the proliferation of connected devices driven by the Internet of Things (IoT) and offers an enhanced feature set to accommodate high-density AP deployments in challenging environments such as smart cities. Supporting data stream rates of up to 10 Gbit/s, the 802.11ax standard boosts spectral efficiency with OFDMA, introduces Uplink MU-MIMO, reduces sub-carrier spacing to increase maximum PHY rates, extends support even to the 2.4GHz band and maximizes power efficiency.